The present invention relates to automatic circuit interrupters and, more particularly, to circuit interrupters or circuit breakers including individual current paths for more than one pole or circuit which are manually resettable and automatically releaseable, simultaneously.
Circuit breakers commonly include a fixed electrical contact and a moveable electrical contact, to which line and load conductors are connected. The moveable contact is connected through a toggle arrangement, such as an overcenter linkage, to a manually operable handle to engage or disengage the moveable contact and the stationary contact, corresponding to closing and opening the circuit breaker, respectively. A particular circuit breaker generally includes one or more circuit responsive releaseable latch mechanisms which automatically cause the stationary and moveable contacts to disengage. These releaseable latch mechanisms may take the form of, for example, bimetallic or other thermal releasing mechanisms, magnetic releases, or solenoid operated releases. When the circuit breaker is to disengage the moveable and the stationary contacts as a result of one or more of the releaseable latching mechanisms functioning, it is desirable that the physical opening of the contacts occur at as rapid a rate as possible. In this regard, the life of the breaker is directly related to the amount of arcing occurring between the contacts as the contacts open, which in turn is related to the amount of time required to separate the contacts.
Often, two or more breaker mechanisms are arranged to be immediately adjacent within a common breaker enclosure for the purpose of protecting electrical circuits having more than one pole or branch. A requirement of such multi-pole circuit breakers is that all poles break the circuit if any one pole is activated by an automatic release mechanism. Simultaneous opening of all poles of a breaker is commonly accomplished by providing a mechanical member between the latching mechanisms of all poles of the breaker, resulting in automatic opening action of any one pole disengaging or unlatching all other poles. When the circuit responsive releaseable latch is present in the circuit breaker as part of the moveable portion of the breaker, connecting adjacent poles for simultaneous tripping is subject to difficulties.
One approach to the coupling of individually moveable latching linkage breakers to provide multi-pole protection involves the use of a common trip bar within an overcenter linkage of the multiple breaker units. The trip bar is connected to a common actuating handle and to each moveable latching linkage through individual pivoted links, one for each pole. A closing force exerted upon the common handle is transmitted to each moving contact assembly through an overcenter toggle linkage assembly including the common trip bar. A device such as discussed immediately above is shown in U.S. Pat. No. 2,923,795 assigned to the same assignee as the present invention. When any one circuit responsive releaseable latch is actuated, that particular pole rotates counterclockwise, in turn applying a counterclockwise force to the common trip bar. Rotation of the trip bar causes movement of pivots of the other overcenter toggle linkages of the remaining poles and results in collapse of the toggle mechanisms. All linkages rotate counterclockwise thus opening current paths substantially simultaneously for all poles.
As the frictional forces between the common trip bar and the handle increase, movement of the handle which is being rotated counterclockwise when closing the breaker, may cause the common trip bar to likewise rotate counterclockwise tending to collapse the overcenter toggle linkages. To overcome this problem, the angle at which the overcenter toggles latch may be increased. The increase, however, may cause the force produced by unlatching one pole to be insufficient at times to collapse the increased overcenter toggle forces of the other poles.
Operation of a circuit breaker in accordance with the above cited patent may be improved by replacing the frictional bearing relationship between the handle and the common trip bar with pivot pins and slots. These pivot pins allow rolling of the common trip bar relative to the handle rather than frictional rubbing. Since the pins and slots define the path through which the common trip bar moves, the initial and final points of this path may be predetermined so as to provide a high overcenter toggle angle at the beginning of movement, with a small angle near the end. Such a device is shown in U.S. Pat. No. 2,923,788 and is assigned to the same assignee as the present invention.
The arrangement of the last mentioned patent provides proper seating of the overcenter links while eliminating the possibility of collapse of the links in fast closing circuit breakers. In slow closing circuit breakers, contact closure occurs very near the midpoint of handle movement where the device of the mentioned patent is still in its high initial overcenter toggle state. If contacts of one pole touch at a point in the closing stroke before the minimal toggle angle has been reached, the tripping force of that one pole may be insufficient to cause collapse of the linkage and simultaneous opening of the other poles.